Process of reducing friction loss in flowing hydrocarbon liquids and compositions thereof

ABSTRACT

The disclosure describes a method of reducing friction during turbulent flow of non-aqueous liquids through conduits by addition to the fluids of from 1 to 2,000 ppm of a novel block polymer comprising chains of a block polymer having the formula A-B wherein A is a high molecular weight polymer block soluble in the hydrocarbon liquid and B is a low molecular weight polymer block substantially less soluble in the fluid.

United States Patent Kruka et al.

Oct. 7, 1975 PROCESS OF REDUCING FRICTION LOSS IN FLOWING HYDROCARBONLIQUIDS AND COMPOSITIONS THEREOF Inventors: Vitold R. Kruka, Houston,Tex;

Dale J. Meier, El Cerrito, Calif,

Assignee: Shell Oil Company, Houston. Tex,

Filed: Mar. 25, 1974 Appl No.: 454,652

Related US. Application Data Continuation of Ser. No. 242,860, April 10,1972, abandoned, which is a division of Ser. No. 156920, June 25, l97l,Pat. Nov 3,687,l48, which is a continuation-impart of Ser No. 5,l56, Jan22. 1970, abandoned.

US. Cl 260/316 AQ; 44/62; 137/l3; 208/370; 252/855 R, 252/59; 260/336 A;260/336 PQ; 260/336 UA; 260/876 B; 260/878 B; 260/879; 260/880 8 Int.Cl. C08K 5/01; FWD l/l6 Field of Search 260/336 AQ, 876 B, 879, 260/880B; 252/855 R, 59; l37/l3; 44/62 [56] References Cited UNITED STATESPATENTS 3.238,l 73 3/1966 Bailey et ul 260/316 A 3.682187 8/1972 Seymouret al. 137/13 $763,044 l0/l973 Anderson w. 252/59 PrimaryExaminer-Donald E. Czaja Assistant ExaminerH. H. Fletcher ABSTRACT 11Claims, N0 Drawings PROCESS OF REDUCING FRICTION LOSS IN FLOWINGHYDROCARBON LIQUIDS AND COMPOSITIONS THEREOF This is a continuation ofapplication Ser. No. 242,860, filed Apr. 10, 1972, and now abandonedwhich is a division of application Ser. No. l56.920 and now U.S. Pat.No. 3,687,l48, filed June 25, I971, which in turn is acontinuation-in-part of application Ser. No. 5,] 56, filed Jan. 22, 1970and now abandoned.

This invention relates to a method of decreasing frictional losses inflowing non-aqueous liquids through conduits, generally over greatdistances, but also over shorter distances such in well-treatingprocesses. More particularly, the invention is directed to the additionof a special class of block copolymers to nonaqueous liquids such ascrude oil and fractions thereof so as to reduce their friction loss dueto flow through pipelines over great and short distances as well as tothe novel compositions of liquid and block polymers dispersed therein.

BACKGROUND OF THE INVENTION It is well known in the art that frictionallosses occurring in the transportation of hydrocarbon liquids ranging inviscosity from about that of gasoline to that of crude oil throughpipelines or other conduits under turbulent flow contribute greatly topumping costs due to increasing energy requirements necessary toovercome this phenomenon. Frictional losses become apparent as apressure drop in the pipeline as the hydrocarbon liquids are pumpedthrough it.

To reduce friction and overcome the undesired effects mentioned above,various means have been tried such as coating of the pipe walls withfriction reducing materials or by addition of friction reducing chemicalagents to the transported liquid. However, these means of reducingfriction have met with little success because of the high cost of eithercoating the pipe walls or that of the friction reducing chemical agentswhich must be added in substantial quantities. Also, the additives arerelatively difficult to disperse in the nonaqueous liquid.

It has also been attempted to employ polymer additives to reducefriction during flow of hydrocarbons through conduits. One difficulty,other than solubility problems, which hampers such use is the sheardegradation or scission of the polymer chains which occurs underturbulent flow conditions. Friction reduction decreases with polymerchain scission because the amount of friction reduction in a given flowdepends strongly on the size of the polymer or polymer agglomerate. Thuswithout repeated injection of prior art polymers substantial frictionreduction can only be obtained in the initial portion of a longpipeline. The present invention not only provides for a high degree ofdispersibility of polymer in the non-aqueous liquid but also overcomesthis undesirable effect of shear degradation. While not restricting thepresent invention to any one theoretical basis, it is hypothesized thatthis is effected by reconstructing the required size polymer throughreassociation of polymer chains once any scission has taken place.Reassociation to form large agglomerates is affected by the affinity ofthe relatively insoluble blocks for each other and the high diffusivityinherent in turbulent flow which will bring the individual chains intothe neighborhood of one another or of agglomerates. Notwithstanding theforegoing, it should be understood that while the above theory isthought to explain the unexpected results found, the invention disclosedis not to be considered bound to any specific theoretical explanation.

SUMMARY OF THE INVENTION The present invention is thus directed towardsa method of reducing friction during the flow of nonaqueous liquidsthrough conduits comprising adding to the liquid hydrocarbon afriction-reducing amount of a highly dispersible polymer which exhibitsminimal effccts of shear degradation consisting of chains of a blockpolymer having the general formula A-B wherein A is a polymer blockhaving an average molecular weight between about 50,000 and 20,000,000or preferably 50,000 and l0,000,000 or more preferably 50,000 and5,000,000 or most preferably from 200,000 to 5,000,000 and soluble inthe liquid and B is a polymer block having an average molecular weightbetween about 500 and 500,000 or preferably 500 and 200,000 or morepreferably 500 and 50,000 or most preferably from 5,000 to 100,000,substantially less soluble (preferably substantially insoluble) in theliquid.

The present invention may also be described a novel compositioncomprising the non-aqueous liquid having dispersed therein a polymer ofthe above description.

The block polymer may be used in concentrations ranging from about I to2,000 ppm (parts by weight of polymer per million parts of liquid) andpreferably from 10 to 500 ppm based on the liquid, which is preferably ahydrocarbon, such as petroleum crude, fractions thereof, liquifiednatural gas or mixtures thereof. The block copolymers may be preparedfrom a wide variety of monomers. Conjugated dienes, for example, whichmay be used in the preparation of the copolymers contain from 4 to 12 or4 to 16 carbon atoms per molecule and preferably the following:l,3-butadiene, isoprene, 2,3-dimethyl-l ,3-butadiene, l,3-pentadiene(piperylene 3-methyll ,3-pe ntadiene, l ,3- heptadiene, 3-butyll,3-octadiene, phenyll ,3- butadiene and the like. Conjugated dienescontaining halogen and alkoxy substituents along the chain can also beemployed such as chloroprene, fluoroprene, 2- methoxyl ,3-butadiene,2-ethoxy-3-ethyll ,3- butadiene, and 3-ethoxy-3-methyl-l,3-hexadiene.Preferred conjugated diolefins to be employed in the present inventionare butadiene, isoprene, and piperylene. Alpha-mono-olefin polymers mayalso be used; an example of monomers from which such polymers may beprepared is polyisobutylene. Other polymers which may be used includelong chain alkyl acrylates and alkylmethacrylates.

Copolymerizable monomers which may be used in the present inventioninclude maleic acids such as maleic anhydrides, vinylpyridines andvinylquinolines in which the vinyl group is attached to a ring carbonother than a carbon in the beta position with respect to the nitrogen.These pyridine, quinoline or isoquinoline derivatives can containsubstituents such as alkyl, cycloalkyl, aryl, alkaryl. aralkyl, alkoxy,aryloxy, and dialkylamino groups in which the total number of carbonatoms in the combined substituents does not exceed 12. Any alkyl groupson the alpha or gamma carbons with respect to the nitrogen should betertiary alkyl groups. Examples of monomers applicable include: 2-

vinylpyridine, 3,5-diethyl-4 vinylpyridine, 3-n-dodecyl-2-vinylpyridinc, 5-cyclohexyl-2-vinylpyridine, 4-phenyl-2-vinylpyridine,3-benzyl-4-vinylpyridine, 6-methoxy-2-vinylpyridine,4-phenoxy-2vinylpyridine,4-dimethylamino-2-vinylpyridine-2-vinylquinoline, 3-methyl-4-ethoxy-2-vinylquinoline, 3vinylisoquinoline,4-phenyl-l-vinylisoquinoline and the like. Other polar monomers includeacrylic and alkyacrylic acid esters, nitriles, and N,N-disubstitutedamides, such as methyl acrylate, ethyl acrylate, butyl acrylate, methylmethacrylate, ethyl methacrylate, propyl methacrylate, butylmethacrylate, methyl ethacrylate, ethyl ethacrylate, isopropylethacrylate; acrylonitrile, methacrylonitrile, N,N-dimethylacrylamide,N,N-diethylmethacrylamide and the like. Vinylfuran and N-vinylcarbazolecan also be used. Other monomers which may be used in the presentinvention are monovinyl arenes such as, for example, styrene and vinyltoluene and other ring substituted styrenes such as alkoxy styrenes(e.g., methoxy styrene) alkyl styrene (e.g., ethyl or diethyl styrene)and as well as haloarenes, particularly halostyrenes (e.g.,2,5-dichlorostyrene). The preferred monomer to be employed in thepresent invention is styrene.

The block copolymers having the above solubility relationships arepreferably selected from the following block types:

a. Conjugated diene polymers.

b. Hydrogenated derivatives of the same.

c. Alpha-mono-olefin polymers and copolymers.

d. Monovinyl arenes copolymerized with conjugated dienes.

e. Hydrogenated derivatives of the same.

f. Monovinyl arenes.

g. Hydrogenated derivatives of the same.

h. Grafted blocks of one type of monomer on the backbone of the secondtype of polymer block.

i. Derivatized block polymers, wherein polymers of the above types havebeen selectiveley or randomly treated to form hydroxyl, carboxyl,sulfonic, amido, amino, etc. derivatives in one or both types of blocks,as well as metal salts of the same.

Hydrogenated derivatives would be of special utility due not only totheir altered solubility characteristics, but also their enhancedthermal and oxidative stability. Hydrogenation may be selective,complete, or random. Thus complete hydrogenation of a relatively highcis polybutadiene-polyisoprene block polymer, for example, gives aderivative closely resembling polyethylene- (ethylene-propylenecopolymer). Mono-alpha olefins may be block copolymerized to form, forexample, polyethylene-EPR or a block polymer-having two random copolymerblocks, having different ratios of monomers chosen to give one solubleand one insoluble block, in the non-aqueous medium being so modified.One, or both mono-alpha olefin blocks can be modified by another type ofcopolymerizable monomer, such as a conjugated diene.

Block copolymers of monovinyl arenes and conjugated dienes are typifiedby polystyrene-polybutadiene and polystyrene-polyisoprene. However,either one or both of the individual blocks may be randomlycopolymerized with a minor (by weight) amount of the other type ofmonomer. Thus, a typical species is polystyrene-(styrene-butadienecopolymer). These may be hydrogenated to alter their individual blocksolubility characteristics as well as to improve their oxidativestability. The hydrogenation may be selective, such as the hydrogenationof polystyrene-polyisoprene to form polystyrene-EPR, or it may becomplete, as in the further hydrogenation of the same block polymer toform polyvinylcyclohexaneEPR. lncomplete non-selective hydrogenation maybe used if desirable for a specific situation.

While end-to-end block copolymers are generally contemplated, it iswithin the scope of the present invention to utilize grafted blockcopolymer wherein the terminal end of one polymer block is grafted to anonterminal carbon atom of the second polymer block. Furthermore, any ofthe above types of block copolymers can be derivatized to alter theirsolubility characteristics or their surface active properties. Thussubstituents may be either terminal groups or positioned along thecopolymer chain in either or both polymer blocks. The proportion of suchnon-hydrocarbon substitutents will vary with the intended function. Suchsubstituents as sulfonic acid, carboxyl, hydroxyl, sulfhydryl, amido,amino, epoxy, cyano, phosphino, aziridinyl, etc. groups may be present.

While the method of preparation of the subject conjugated diene blockpolymers forms no part of the present invention, they may be preparedfor the most part by conventional methods. A preferred process to beused in the present invention is the so-called sequential process whichmay be described, by way of illustration, as follows: A conjugated dienehydrocarbon such as butadiene is subjected to solution polymerization inthe presence of a lithium based catalyst, such as lithium alkyl.Polymerization is conducted to the point where the first polymer blockis formed, after which, without termination of the growing polymerchains, a copolymerizable monomer such as styrene is injected andpolymerization is continued. in the se quential process, polymerizationis conducted until the desired molecular weight of the entire secondblock is formed. The products obtained having the general configurationA-B, wherein A is an essentially unbranched polymer block of aconjugated diene (in this case, polybutadiene) while B is a polymerblock of a copolymerizable monomer (in this case, polystyrene). By"essentially unbranched is meant a polymer block which does nto containregularly spaced or regularly oriented hydrocarbon substitutents pendantfrom the backbone of the polymer chain.

The block polymers so obtained can be substantially hydrogenated so thatat least about of the double bonds in the original block copolymer andpreferably in excess of about are hydrogenated.

The type of catalyst employed for the production of alpha olefin blockcopolymers is of some importance in obtaining the optimum propertiesdesired for such compositions. The usual Ziegler catalysts, such astitanium halides and the like may be employed for this purpose togetherwith aluminum halides or aluminum organo halides. It is preferred to use5-l .500 millimoles of titanium and 105,000 millimoles of aluminum perliter of total reaction mixture. The preferred types of catalyst are thevanadium based polymerization catalysts used in conjunction withaluminum-containing reducing agents. Preferred among these are threegeneral classes of vanadium compounds, namely, those based upon vanadiumalkoxides, vanadium salts of salicylic acids and vanadium salts ofsulfonic acids. The molecular ratio in which the catalyst components arepresent has a powerful influence upon both the rate and yield of thepolymerization and on the properties of the polymer. In general, thenumber of atoms of vanadium and the number of aluminum atoms are in aratio varying from about 0.51:1 and 2:1. In general, the highest yieldsand most desirable molecular weights are obtained when this ratio isbetween about 0.05: 100 millimoles of vanadium and 0.550 millimoles ofaluminum per liter of reaction mixture. Another type of synthesiscomprises the polymerization of a polymer block A bearing a functionalgroup, e.g., carboxyl and a second polymer block B bearing a functionalgroup reactive with that of block A, e.g., hydroxyl, and reacting thetwo to form a block copolymer with an insignificant linkage, e.g.,ester, resulting from the reaction.

The block copolymerization is conducted in the presence of a solvent(e.g., hydrocarbon) which is essentially inert under the conditions ofthe polymerization. Alkanes and cycloalkanes such as hexane,cyclohexane, heptane, or other saturated hydrocarbons having from 4-10carbon atoms per molecule are preferred solvents for this purpose.Aromatic solvents, benzene, toluene, etc., also can be sued as well assome chlorinated alkanes and cycloalkanes. These solvents may bemodified by the additional presence of 05-10% by weight of achlorocarbon such as carbon tetrachloride.

The polymerization is to be conducted under conditions which will avoidinadvertent termination of the growing polymer chain. This temperaturerange is usually between about 25C and 100C the preferred range beingbetween about l5C and 75C.

To illustrate the manner in which the invention may be carried out, thefollowing examples are given. It is to be understood, however, that theexamples are for the purpose of illustration and the invention is not tobe regarded as limited to any of the specific conditions cited therein.

EXAMPLE 1 Preparation of Butadiene Styrene Block Polymer 30 Partsstyrene was subjected to solution polymerization in 800 partscyclohexane containing 0.00037 mols butyl lithium polymerizationcatalyst. The reaction was run at 50C until all of the styrene hadpolymerized, (about 1% hours). Then 251 parts butadiene in 2,000 partscyclohexane was injected and polymerization continued for about 3% hoursat 60C until all of the butadiene had polymerized. The resulting blockpolymer had molecular weights as follows: Polystyrene block, about24,000; polybutadiene block, about 715,000.

EXAMPLE [I A block polymer is prepared from butadiene andmethylmethacrylate in the manner disclosed in Example l. The final blockpolymer has the configuration polybutadiene-polymethylmethacrylate, theaverage molecular weight of the polybutadiene polymer block being about500,000 and the average molecular weight of the polymethylmethacrylatepolymer block being about 30,000.

EXAMPLE lll Hydrogenation of Conjugated Diene Block CopolymersHydrogenation of the polymer prepared according to Example 11 iseffected in the presence of a catalyst prepared by contacting nickelacetate with aluminum triethyl, in a molar ratio of 1.5: l alunummickel.The catalyst components are heated in cyclohexane for 30 minutes at130C. An amount of catalyst sufficient to provide 1% by weight ofreduced nickel based on the polymer is suspended in a cyclohexanesolution of the polymer, the solution containing 14% by weight of thelatter. The reactor is pressured to 1500 psig with hydrogen and heatedto a maximum of 140C with polymer, the solution containing 14% by weightof the latter. The reactor is pressured to 1500 psig with hydrogen andheated to a maximum of 140C with vigorous stirring. The total reactiontime is 140 minutes minutes above Absorption of hydrogen takes placeimmediately and is probably completed within 30 minutes. The finalreaction pressure at C is l 120 psig. The product is essentiallycompletely hydrogenated and has the configurationpolyethylene-polymethylmethacrylate.

EXAMPLE [V Example 1 is repeated except ethylene oxide is used as thecopolymerizable monomer instead of styrene. A block polymer having thestructure polybutadienepolyethylene oxide is produced wherein thepolyethylene oxide block has an average molecular weight of 2,000.

EXAMPLE V The composition of Example 1 was tested and compared with apolyisobutylene sample of an approxi mately equivalent molecular weight.Both samples were tested at a concentration of 268 ppm in cyclohexane.The test system consists of a 4-foot long 0.143- inch l.D. glass tubewith pressure taps located 7 inches apart in the fully developed portionof the flow. The sample solution is circulated through the system bymeans of two S-inch diameter pistons at the opposing ends of the glasstube. This method of pumping the solutions eliminates shear degradationof the polymers which takes place in conventional pumps.

The solutions were recirculated through the flow system at a Wall shearstress of 5600 dynes/cm' The wall shear stress is given by F=100 m n/nwhere j and f are the solvent and solution friction factors respectivelyand read as 1 (it 2 p LH where p and U are the density and bulkvelocity.

TABLE I Percent Friction Reduction 268 ppm Styrene-Butadiene 268 ppmPolyisobutylene As can be seen, the styrene-butadiene block copolymer ismore effective in reducing firctional losses than polyisobutylene. Theinitial degrees of friction reduction for the styrene-butadiene andpolyisobutylene are 70.5% and 48.4% respectively. Further, thestyrenebutadiene block copolymer maintains its ability to reducefriction better than polyisobutylene. After 700 passes through thesystem the two solutions yield friction reductions of 34.9% and 14.7%.That is, the styrene-butadiene has lost 50.5% of its initial frictionreducing capability while the polyisobutylene displays a loss of 69.7%.

The degree of friction reduction is strongly dependent on the effectivesize of the polymer molecule or polymer agglomerate. This dependencemanifests itself 0 in the onset conditions for friction reduction.Usually the onset condition is expressed in terms of a critical wallshear stress, w/cr. This critical wall shear stress decreases withincreasing polymer size. Friction reduction can be obtained only if thewall shear stress existing in any given flow exceeds the critical wallshear stress. Thus it is desirable to have large polymers and lowcritical wall shears. The onset conditions for conventional polymers areindependent of polymer concentration. The styrene-butadiene blockcopolymer, on the other hand, displays a lower critical wall shearstress with increased concentration. Table ll serves to demonstrate thisbehavior:

major part to the phenomena referred to earlier: The relatively highmolecular weight block, being miscible with the non-aqueous liquid,enables the polymer to be dispersed in the liquid. The relatively lowmolecular weight block, being substantially less soluble (or eveninsoluble) in the liquid, tends to associate with similar blocks fromother polymer chains, thus forming domains, variously referred to asaggregates or agglomerates. The forces holding such domains together arephysical rather than chemical; and, upon stress due to high shear at thepipe wall, the domains may disintegrate. However, at a later pointdownstream when the polymer may be in a position or environment ofreduced shear, the domains may reform and the function of the polymer asa friction reducing agent is reestablished. Normal high molecular weightpolymers, such as polyisobutylene, for example, exhibit the cleavage ofchemical bonds under conditions of high shear. Such cleavage isirreversible and consequently effectiveness of such polymers as frictionreducing agents decreases at a rate relative to the stability of thepolymer to shear degradation.

The primary types of utility of the present invention are in pipelinetransportation of non-aqueous fluids from one geographical location toanother and in injection of drilling fluids or oil well treating fluids.The first of these involves relatively horizontal pipelines, con- Thebenefit gained by the use of the present invention lies in thesubstantial friction reducing ability during turbulent high speed orhigh pressure flow through pipelines, and the maintenance of thisability over a long period even though subject to high shear conditions.As stated hereinbefore, ordinary polymers, such as polyisobutylene andthe like exhibit more catastrophic chain scission under similarconditions.

While the precise reason for the outstanding performance of the presenttwo-block copolymers has not been completely elucidated, it is believedto be due in forming to landscape contours, and passage of the liquids,e.g., liquid or liquified hydrocarbons, through pumping stations toterminals such as shipping facilities, tankers, refineries, etc. Thereduction in frictioncaused pressure loss in an important economicfactor in such situations.

The use of the invention in oil-based drilling fluids and well treatingfluids (a relatively vertical tubing being involved) also is ofsubstantial benefit since high pressures and turbulent flows areinvolved.

We claim:

1. A composition for reducing friction in a conduit transporting crudeoil comprising liquid crude oil having dispersed therein from 0.000] to0.2 weight percent of a two-block copolymer wherein a block A is substantially soluble in the liquid crude oil and has an average molecularweight between about X and 2 X 10', and a block B is substantially lesssoluble in the liquid crude oil and has an average molecular weightbetween about 5 X 10 and 5 X 10.

2. A composition according to claim I wherein the liquid is ahydrocarbon, block B predominates in polymerized monovinyl arene unitsand the block A predominates in polymerized conjugated diene units.

3. A composition according to claim 1 wherein the liquid is ahydrocarbon, the block B comprises a alpha olefin homopolymer block andthe block A comprises a copolymer block of at least two alpha olefins.

4. A composition according to claim 1 wherein block A is a hydrogenatedpolyisoprene block and block B is a hydrogenated poiybutadiene block.

5. A composition according to claim 1 wherein block B is a polystyreneblock and block A is a polybutadiene block.

6. A composition according to claim 1 wherein block B is a polymaleicacid block and block A is a polybutadiene block.

7. A composition according to claim 1 wherein block B is a vinylpyridineblock and block A is a polybutadiene block.

8. A composition according to claim 1 wherein block B is substantiallyinsoluble in the liquid medium.

9. A composition for reducing friction in a conduit transporting crudeoil comprising liquid crude oil having dispersed therein from 0.000] to0.2 weight percent of a two-block copolymer wherein block A ispolybutadiene and block B is polymaleic acid.

10. A composition for reducing friction in a conduit transporting crudeoil comprising liquid crude having dispersed therein from about 0.0001to 0.2 weight percent of a two-block copolymer wherein a block A ispolybutadiene and block B is polyvinylpyridine.

H. A composition for reducing friction in a conduit transporting crudeoil comprising liquid crude oil having dispersed therein from 0.000! to0.2 weight percent of a two-block copolymer wherein a block A issubstantially soluble in the liquid crude oil and has an averagemolecular weight between about 5 X 10 and 2 X 10, and a block B issubstantially insoluble in the liquid crude oil and has an averagemolecular weight between about 5 X 10 and 5 X l0".

1. A COMPOSITION FOR REDUCING FRICTION IN A CONDUIT TRANSPORTING CRUIDEOIL COMPRISING LIQUID CRUDE OIL HAVING DISPERSED THEREIN FROM 0.0001 TO0.2 WEIGHT PERCENT OF A TWO-BLOCK COPLYMER WHEREIN A BLOCK A ISSUBSTANTIALLY SOLUBLE IN THE LIQUID CRUDE OIL AND HAS AN AVERAGEMOLECULAR WEIGHT BETWEEN ABOUT 5?10**4 AND 2?10**7, AND A BLOCK B ISSUBSTANTIALLY LESS SOLUBLE IN THE LIQUID CRUDE OIL AND HAS AN AVERAGEMOLECULAR WEIGHT BETWEEN ABOUT 5?10**2 AND 5?10**5,
 2. A compositionaccording to claim 1 wherein the liquid is a hydrocarbon, block Bpredominates in polymerized monovinyl arene units and the block Apredominates in polymerized conjugated diene units.
 3. A compositionaccording to claim 1 wherein the liquid is a hydrocarbon, the block Bcomprises a alpha olefin homopolymer block and the block A comprises acopolymer block of at least two alpha olefins.
 4. A compositionaccording to claim 1 wherein block A is a hydrogenated polyisopreneblock and block B is a hydrogenated polybutadiene block.
 5. Acomposition according to claim 1 wherein block B is a polystyrene blockand block A is a polybuTadiene block.
 6. A composition according toclaim 1 wherein block B is a polymaleic acid block and block A is apolybutadiene block.
 7. A composition according to claim 1 wherein blockB is a vinylpyridine block and block A is a polybutadiene block.
 8. Acomposition according to claim 1 wherein block B is substantiallyinsoluble in the liquid medium.
 9. A composition for reducing frictionin a conduit transporting crude oil comprising liquid crude oil havingdispersed therein from 0.0001 to 0.2 weight percent of a two-blockcopolymer wherein block A is polybutadiene and block B is polymaleicacid.
 10. A composition for reducing friction in a conduit transportingcrude oil comprising liquid crude having dispersed therein from about0.0001 to 0.2 weight percent of a two-block copolymer wherein a block Ais polybutadiene and block B is polyvinylpyridine.
 11. A composition forreducing friction in a conduit transporting crude oil comprising liquidcrude oil having dispersed therein from 0.0001 to 0.2 weight percent ofa two-block copolymer wherein a block A is substantially soluble in theliquid crude oil and has an average molecular weight between about 5 X104 and 2 X 107, and a block B is substantially insoluble in the liquidcrude oil and has an average molecular weight between about 5 X 102 and5 X 105.